CHAPTER IX. 



NUTRITION, DIETETICS AND ANIMAL HEAT. 

 NUTRITION. 



ALL the processes of the body as digestion, absorption, se- 

 cretion, circulation, respiration, etc. have a single object, 

 viz., the nutrition of the cells of the body. 



The ultimate source of all nutriment is, of course, food 

 and oxygen. The oxygen has been followed from the lungs 

 to the tissues as oxyhemoglobin of the blood. The various 

 foods have been seen to disappear from the digestive tract 

 and to be conveyed to the tissues by the great nutritive fluid, 

 some in recognizable and some in unrecognizable form. If, 

 now, we shall be able to discover in what way these different 

 materials thus furnished the cells are utilized and appropri- 

 ated by them, and in what condition they subsequently es- 

 cape from the system, the study of nutrition will have been 

 rendered much clearer. The intake is through the lungs and 

 alimentary canal ; the output is mainly by the lungs, skin, kid- 

 neys, and intestines. To show for the changes which take 

 place while the food is in the body there is the growth of the 

 body, the maintenance of tissue integrity, secretion, heat, 

 motion and nervous energy. 



It may be said at once, however, that the exact method of 

 appropriation of nutritive material by the tissues is a sub- 

 ject of speculation, since it involves the question of life 

 itself ; and we shall have to be content with recounting some 

 of the conditions influencing and some of the phenomena 

 attendant upon the process. 



171 



